Apparatus including transmitter, receiver and display housings for locating corresponding points on opposite sides of a structure

ABSTRACT

A method and apparatus for locating two corresponding points on opposite sides of a wall, floor, or other structural component. A transmitter transmits a electromagnetic signal indicative of a first point located on one side of the component, a signal receiver on the other side of the component generates an electrical signal proportionate to the strength of the electromagnetic signal, and a display outputs a maximum reading when the signal receiver indicates a maximum electromagnetic signal. The sensitivity of the display may be adjusted. The transmitter, receiver, and display may be structurally integrated when not in use. The transmitter is attached to the first side of the structural component at the first point, the receiver is moved along a second side of the structural component, and the receiver is moved along the second side to a location indicated by a maximum display.

BACKGROUND OF THE INVENTION

The present invention relates generally to a method and apparatus forlocating points, and more particularly, to a method and apparatus forlocating two corresponding points on opposite sides of a wall, floor, orother structural component.

Plumbing and heating contractors, carpenters, electricians, T.V. cableinstallers, and other persons working on structural components such aswalls and floors often have a need to locate points corresponding toeach other along a selected linear path on either side of the walls orfloors. For example, it is sometimes necessary to drill a hole from oneside of a wall through to the other side in a manner which ensures thatthe hole will be in the proper location on both sides of the structuralcomponent.

Since the points often cannot be viewed simultaneously, conventionalmethods of locating the corresponding points on either side of thestructural component involve making measurements from floors or otherfixed points. However, these conventional measurement methods frequentlyresult in substantial errors in identifying the corresponding points.These inaccuracies in conventional measuring techniques may result inmisidentification of objects or restrictions on one or both sides of thesurface.

SUMMARY OF THE INVENTION

The apparatus in accordance with the present invention for locating twopoints corresponding to points located on the opposite sides of astructural component comprises a transmitter housing for enclosing asignal transmitting means for transmitting a preselected electromagneticsignal attachable to one side of the structural component, a signaltransmitting means mounted in the transmitter housing for transmittingan electromagnetic signal having a preselected frequency and indicativeof a first point located on the first side of the structural componenthaving a location at a predetermined spacial relationship to thetransmitter housing, a receiver housing for enclosing a signal receivingmeans, a signal receiving means mounted in said receiver housing forgenerating an electrical signal proportionate to the strength of theelectromagnetic signal received from the transmitting means at apredetermined second point located on the second side of the structuralcomponent at a predetermined spacial relationship to said receiverhousing, display means for displaying a maximum reading when saidelectrical signal generated by said signal receiving means indicates amaximum electromagnetic signal level, such that a maximum reading isdisplayed at the display means when the first point and second point arelocated along a line substantially normal to the face of thetransmitting means, and electrical interconnecting means forelectrically interconnecting the signal receiving means to the displaymeans.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an apparatus in accordance with the present inventionincluding a transmitter, a receiver, and a display device as used on astructural component;

FIG. 2 is a top and front-left perspective of a precision locatorapparatus in stored form in accordance with the present invention;

FIG. 3 is a top and left-rear exploded perspective of a precisionlocator apparatus detached for use in accordance with the presentinvention;

FIG. 4 is a bottom plan view of an apparatus in accordance with thepresent invention, the side opposite that shown being a mirror imagethereof;

FIG. 5A is a right side elevational view of an apparatus in accordancewith the present invention in stored form, the side opposite that shownbeing a mirror image thereof;

FIG. 5B is a rear elevational view thereof;

FIG. 5C is a bottom plan view thereof, the side opposite that shownbeing a mirror image;

FIG. 5D is a right side elevational view of a transmitter disengagedfrom the display housing in accordance with the present invention;

FIG. 6 is a block diagram showing the components of the transmitter,receiver, and amplifier/display circuitry in accordance with the presentinvention;

FIG. 7 is a diagram showing a method of locating two points on oppositesides of a structural component in accordance with the presentinvention;

FIG. 8A is a top and rear perspective view of a transmitter to besecured in position by a nail in accordance with the present invention;

FIG. 8B is a top and rear perspective view of a transmitter taped inposition in accordance with the present invention;

FIG. 8C is a top and rear perspective view of a transmitter to be taped,in position in accordance with the present invention;

FIG. 9 is a diagram including a tracing around a receiver housing(notshown) for showing a method of locating a point in accordance with thepresent invention;

FIG. 10 is a side elevational view of a separated transmitter housing inaccordance with the present invention;

FIGS. 11A and 11B are schematic diagrams of the transmitter, receiver,and amplifier/display circuits of the present invention;

FIGS. 12A and 12B are top views of the liquid crystal display elementand cover thereof in accordance with the present invention; and

FIG. 13 is a diagram of a variation on a method of locating two pointson opposite sides of a structural component in accordance with thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows an apparatus in accordance with the present invention asused on a structural component such as walls 16 and 18. The apparatusincludes a transmitter 10, a receiver 12, and a display device orhousing 14. In the preferred mode of use, the transmitter 10 includes asignal transmitting means such as a transmitter enclosed in atransmitter housing, which is placed flush to the surface of astructural component such as wall 18 by way of transmitter housingsurface 20. The transmitter emits an electromagnetic signal representedby circles 24 which is received by a receiver 12 which includes areceiver mounted in a receiver housing on the opposite side of thestructural component along wall 16. Receiver 12 is also placed flushagainst the opposite surface of the structural component in the typicalmode of use. Receiver 12 is electrically interconnected with displaydevice 14 by means of an electrical interconnecting means such aselectrical cord 26. The use of electrical cord 26 allows for greaterflexibility in moving the receiving housing 12 to a desired location,and allows for reading the display at a convenient angle remote from thedisplay housing regardless of the angle required for proper use of thereceiver.

Display housing 14 receives an electrical signal from receiving means 12which is proportionate to the strength of the electromagnetic signalreceived from transmitter 10. The receiver 12 is moved along wall 16 toa location which indicates a maximum electromagnetic signal, typicallyindicating the closest location on wall 16 to transmitter 10. Suchlocation will enable the precise location of two corresponding points oneither side of walls 16 and 18, especially when the transmitting andreceiving surfaces of transmitter 10 and receiver 12 are directly facingeach other.

The external structure of an apparatus in accordance with the presentinvention is shown in greater detail in FIGS. 2 through 5C. FIG. 2 showsa point locator 30 in a stored position, comprising transmitter 10,display device 14, and receiver 12. Display device 14 includes a visualdisplay 34 which, in the embodiment shown, comprises a liquid crystaldisplay including a succession of parallel bars which increase in numberas the signal received by the receiver gets stronger. Also shown in FIG.2 is sensitivity control 38 for controlling a sensitivity adjustingmeans described in greater detail below. By activating this sensitivitycontrol, ordinarily manually by the push of a button, as shown, thedisplay 34 is reset to an output between the minimum and maximum displayreadings, even if the display previously indicated a minimum or maximumdisplay. This allows more accurate location of the receiver relative tothe transmitter, since the output may be repeatedly readjustedsubstantially independently of the distance between the transmitter andreceiver. Sensitivity increases as the receiver gets closer to thetransmitter. FIG. 2 also shows holes 52 and 56 formed in display housing14 for receiving receiver retainer 42 and transmitter retainer 46.

FIG. 3 shows the transmitter, receiver, and display components inaccordance with the present invention in a detached form ready for use.The display means 14 forms holes 52 and 56 for receiving receiverretainer 42 and transmitter retainer 46, respectively. Electrical cord26 is shown plugged into the display housing at display jack 60. Theelectrical cord 26 is plugged into the receiver at receiver jack 64.This cord provides the electrical interconnection between the receiverhousing and the display housing and turns the receiver and the displayon. Physically detaching the receiver from the display means whilemaintaining an electrical connection between the two components allowsthe display to be held at a convenient viewing angle regardless of thelocation needed for the receiver. This features also allows for easieruse of the locating device in confined areas.

The transmitter 10 includes an insertable portion 68 for inserting intoone hollow end of display means 14, and a base portion 70 which isslightly larger than the insertable portion and which is slid intoposition flush with the display device 14 when the insertable portion 68is inserted into the display device. Receiver 12 has a structure similarto transmitter 10, including an insertable portion 74 and a base portion76.

FIG. 4 shows an end view of the base portion 70 of transmitter 10, whichis identical to the base portion 76 of receiver 12. The face shown inFIG. 4 is surface 20, also shown in FIG. 1. This surface is the surfacefrom which the electromagnetic signal is emitted by the transmitter. Toenhance precise location of the transmitter on one side of thestructural component, a nail receiving means such as a nail slot 80 isformed in surface 20. Transmitter 10 may be centered on a position on astructural component by inserting a small nail into the surface at thepoint to be located, and hanging the transmitter by slot 80 to thesurface of the structural component. A transmitter slid into positionover a nail as described is shown in FIG. 8A. The position of the nailwhen slid along slot 80 is the position closest to the electromagneticsignal in the preferred embodiment, preferably but not necessarily nearthe center of surface 20.

Where it is not desirable to insert a nail into a surface, such as wherethe surfaces of the structural component are too hard to receive nails,the planar surface 20 of transmitter 10 may be attached to a structuralcomponent by single sided tape 23, 24 or double sided tape 25, shown inFIGS. 8B and 8C, respectively. Slots such as slot 81 in FIGS. 8A and 8Bprovide exterior markings to the transmitter and receiver housings suchthat the center of the housings may be aligned when the housings areplaced flush against a flat surface.

FIG. 5A shows components of the apparatus 30 of the present invention,including a view of a display means such as liquid crystal display 34,structurally integrated for convenient storage when not in use. Alsoshown is sensitivity control 38. As discussed with respect to FIG. 4,slots such as slots 80 and 87 in FIG. 5B may be used to receive a nailmounted in a wall to hold the transmitter and receiver units,respectively, to the wall.

FIG. 5B is yet another view of the structurally integrated componentmodule 30 comprising transmitter housing 10, receiver housing 12, anddisplay housing 14 in accordance with the present invention. Displayhousing 14 is formed by an extrusion process which results in theformation of the three sides of the display housing other than the sidehaving LCD 34 shown in FIG. 5A. The three sides are snapped around theLCD side, which is separately fabricated. Shown is display device jack60 without an electrical cord inserted therein, and receiver jack 64also without an electrical cord inserted therein. Also shown is thetransmitter strength control means in the form of control switch 84 ofthe transmitter including a central off position 86, as shown, a high orstrong signal emitter position 88, and a low or weaker signal positionindicator 90. This switch may be manually operated such that thetransmitter produces no signal at all, a relatively weaker signal, or arelatively stronger signal for receipt by the receiver means. Thestronger or weaker signal may be chosen in accordance with how thick thestructural component is, or the materials composing the structuralcomponent, or to increase or decrease receiver sensitivity, among otherfactors. FIG. 5C shows a side view of the transmitter, receiver, anddisplay housings joined, as previously discussed with respect to FIG. 2.

FIG. 5D is a more detailed presentation of the means for connecting andseparating transmitter 10 from display housing 14. Transmitter 10,having a connecting and separating structure similar to receiver 12, hasa pair of releases indicated by 42 and 42' located on opposite sides ofthe transmitter. When the transmitter is stored with the displayhousing, the ends of retainers 42 and 42' are stored in display housingretainer receiving holes 52 and 52', respectively. To release thetransmitter from the display housing, retainers 42 and 42' are depressedthrough retainer receiving holes 52 and 52', in the direction indicatedby the arrows 54 and 54'. This releases the transmitter from the displayhousing and allows the insertable, narrower portion 68 of thetransmitter to be slid out of the display housing. The wider baseportion 70 abuts the display housing 14 when transmitter housing 10 anddisplay housing 14 are completely integrated. Each end of displayhousing 14 forms a cavity, one for receiving the insertable portion 68of the transmitter housing and the other for receiving the correspondingportion of receiver housing 12.

FIG. 6 is a block diagram of the electrical circuitry of an apparatus inaccordance with the present invention including a transmitter 100, areceiver 120, and an amplifying and display circuit- 140. Transmitter100 is powered by a nine volt battery 102 which may be replaced asneeded, in a manner to be described below. The power is controlled atpower switch 104, which may take a high, low, or off position asindicated in FIG. 5B at switch 84. Oscillator 106 creates an electricalsignal which is converted into an electromagnetic signal of apredetermined frequency at transmit coil (transformer) 108.

The electromagnetic signal 24 is received by the receiver 120 at pick-upcoil (transformer) 122. The electromagnetic signal is converted into anelectrical signal and amplified by preamplifier 124. This circuitry isalso powered by a nine volt battery 126. The receiver element isinterconnected to the amplifier/display circuit 140 by electrical wires128, 128', 118, and 118', which are interconnected between receivercircuit 120 and amplifier/display circuit 140 by cord 26, discussedpreviously. Connection of cord 26 to receiver housing 12 and displayhousing 14 supplies power to amplifier/display circuit 140 by way ofline 128'. The interconnection and function of lines 118, 118', 128, and128' are shown and described in more detail in FIG. 11B and accompanyingtext. Amplifier/display circuit 140 is powered by the same nine voltsource 126 that powers the receiver element 120. The amplifier/displaycircuit provides a return line for this power source through line 128 toreceiver circuit 120. Detector diode 130 ensures that a negative voltagepotential is not provided across adjustable gain DC amplifier 132. Theelectrical signal received from receiver element 120 is amplified atadjustable gain DC amplifier 132. This amplification may be adjusted bysensitivity control 134, corresponding to control 38 in FIG. 5A.Successive activations of the sensitivity switch 134 successively adjustthe gain provided by the DC amplifier 132 such that the reading atliquid crystal display(LCD) 34 is between the minimum and maximumreadings, and preferably at a middle-range reading. The signal isfurther amplified by amplifier 136 and converted into a signal readableat the liquid crystal display 34 by means of the display driver circuit138.

A method of locating two corresponding points on either side of astructural component will now be described in greater detail. Thedevice, shown in stored form in FIG. 2, is separated into components foruse as described in connection with FIG. 5D. By applying pressure to theretainers, the receiver 12 and transmitter 10 are loosened from thedisplay housing 14 such that they may be easily slipped out of thehousing as shown in FIG. 5D. Once the components are separated and cord26 is inserted into jacks 60 and 64, the apparatus takes the form shownin FIG. 3. Plugging the cord 26 into receiver jack 64 automaticallyturns the receiver and display circuits on.

Switch 84 of transmitter 10 is then activated to generate anelectromagnetic signal. The high output position is normally used forstructural thicknesses ranging from 12 to 36 inches. The low outputposition is used for structural component thicknesses of 3 to 12 inches,and allows for the greatest alignment accuracy. The high setting may,however, provide quicker general location for any thickness.

Before using the apparatus with a structural component, the deviceshould be tested and adjusted. This is done by setting the transmitterto its low setting and placing it on a flat surface. The receiver shouldbe held at a position remote from the transmitter, and the displayviewed. This initial step should be done with the transmitter andreceiver located a few feet from each other. The sensitivity switchshould then be pressed and released to obtain the initial sensitivityrange. The face of the receiver, corresponding to surface 78 shown inFIG. 3, should be moved towards the face 20 of transmitter 10. Thedisplay means 34 will indicate an increasingly strong signal. When thedisplay means indicates a maximum signal, the receiver should be held inposition as the sensitivity switch 38 is activated. Pressing thesensitivity switch resets the display readout to a lower level whichremains proportionate to the electromagnetic signal strength received atthe receiver, and limits the apparatus's range to shorter distances.However, sensitivity within that shorter distance range increases forgreater accuracy.

FIG. 7 shows an apparatus in accordance with the present invention asused step-by-step to indicate the desired locations. The transmittingsurface 20 of transmitter 10 is centered over first location A locatedon the side of surface 18 opposite the surface 16. Typically, surface 18is a flat surface and the corresponding point B will be located on theopposite side of wall 16 from wall 18 along a line from point Aperpendicular to the surface of wall 18. However, it should be clear toone skilled in the art that the method and apparatus described hereinmay be used to align points A and B which are not perpendicular to eachother. Surfaces 16 and 18 may comprise portions of other structuralcomponents such as a floor. Transmitter 10 is set to either the LOW orHIGH setting, depending on the structural thickness and accuracydesired.

Receiver 12 having a signal receiving surface 78 is shown in FIG. 7 insuccessive locations including locations centered over points X, Y, B,and Z leading to a final location corresponding to desired point B. Oncethe display readout 34 is calibrated, it will have a relatively lowreading, represented by display reading 160, when transmitter 12 iscentered over location X on wall 16. Transmitter 12 is then moved alongwall 16 in a direction corresponding to a stronger electromagneticsignal output at display 34. In FIG. 7, this is represented by thereceiver 12 located over point Y. When receiver 12 is moved in thedirection closer to desired point B, represented by receiver 12', thesignal reading displayed in display readout 34 will increase instrength. Should the sensitivity of display readout 34' be set too high,the reading at point Y may be a maximum reading, as shown in display162, even though the receiver is not yet centered over optimum point B.Thus, should the maximum readout appear as in display readout 162,sensitivity control 38 should be depressed to obtain a lower reading forthe same point, as indicated by display readout 164 for point Y. Thereceiver 12' is then again moved in a direction indicating a strongersignal, in FIG. 7 from point Y to desired point B. When receiver 12" iscentered over location B, the readout displayed in display 34" may takethe form as shown in display 166, indicating a stronger signal then thatshown in display 164 for point Y (after sensitivity is adjusted) but asignal below the maximum level which may be displayed by the displayreadout.

As receiver 12", is moved past optimum point B to location Z, theelectromagnetic signal from transmitter 10 will again weaken and thedisplay readout 168 will indicate a lower signal than that indicated bydisplay 166 for point B. This lower display readout indicates that thereceiver 12'" has gone past optimum point B and should be moved backfrom point Z to point B. By this method, the receiver 12 may provide anindication of point B within an accuracy of as little as 0.25 inch.

Once the receiver 12" is centered over location B, the point may bemarked for reference by the user. A simple means of locating point B isshown in FIG. 9. FIG. 9 shows an outline 180 drawn around the peripheryof receiving face 78 of receiver 12. Face 78 is structurally integratedwith the receiver housing 12, formed in the periphery thereof, and maybe identical to the shape of the transmitting surface 20 shown in FIG.4. Once the tracing 180 is completed, receiver 12 may be removed fromsurface 16. The tracing 180 has a number of sides which areconsecutively joined at connecting points 182, 184, 186, 188, 190, 192,194, and 196. The receiving surface 78 of receiver 12 is designed suchthat lines drawn between at least two appropriate pairs of these pointswill intersect the center of the receiving surface, corresponding topoint B in FIG. 7. For example, lines drawn from point 184 to point 192,and point 186 to 194, as shown at L1 and L2, will intersect at point B.Corresponding connecting points may be labeled, but it will be evidentto one skilled in the use of the apparatus which points correspond toeach other. In this manner, point B may be located with substantialprecision. It should be obvious to one skilled in the art that variousother shapes of receiver surface 78 may be used which would generate adifferent shape for tracing 180 but which would still indicate locationB with substantial precision in a manner similar to that describedherein.

FIG. 10 shows how the transmitter 10 may be opened in order to insert orchange the battery for the transmitter. Receiver 12 has a similarconstruction. Retainers 42 and 42' may be pulled away from the narrowportion 68 of receiver 10. Such movement of retainers 42 and 42, resultsin releasing the base portion 70 of transmitter 10 from the narrowportion 68, exposing the inside of the transmitter where the battery islocated.

FIGS. 11A and 11B are schematic drawings of the transmitter, receiver,and amplifier/display circuitry shown more generally in FIG. 6.Transmitter 100, shown in FIG. 11A, includes 9 volt source 102. Diode D1provides reverse-polarity protection, for example, from incorrectlyconnecting the battery. The power source feeds through resistor R1 topower switch 104, previously described.

The HIGH and LOW settings of power switch 104 are regulated by two zenerdiodes D4 and D5. D4 may have a reverse-bias voltage of 2.4 V and aforward-bias voltage of 0.6 V, and D5 may have a reverse-bias voltage of3.3 V. At the HI power setting, both D4 and D5 are reverse biased andthe power output is 2.4 V plus 3.3 V or 5.7 V. At the LO power setting,D4 is forward-biased and D5 is reverse-biased. The voltage potential atthe forward end of D4 is 3.3 V minus 0.6 V, or 2.7 V. The output ofswitch 104 regulates the base of transistor Q2.

Power source 102 also feeds the collector of transistor Q2. TransistorQ2, in conjunction with resistor R5, capacitors C1, C2, and C4, diodeD2, and transistor Q1, produce an oscillating signal emitted bytransmitter coil (transformer) 226. Resistor R2 and forward-biased diodeD3 provide a sufficient forward-biasing voltage to transistor Q1 tomaintain the transistor in its amplification mode. A typical operatingfrequency that may be selected for the transmitter circuit is 7.932 KHz.

The signal emitted by the transmitter 100 is received at receiver 120through pickup coil (transformer) 122, shown in FIG. 11B. Capacitors C5and C6, in tandem with pick-up coil L1, have capacitances selected forreceipt of electromagnetic signals of the frequency generated by thetransmitter. Capacitor C7 decouples coil (transformer) L1 from ground toprevent short-circuits.

The signal generated by coil L1 is amplified by the circuit comprisingthe nine-volt battery source 126 protected from reverse polarity bydiode D7, capacitor C8, and transistors Q3, Q4, and Q5. Resistors R8 andR9 provide loads for the collectors of Darlington-pair transistors Q3and Q4. Resistor R7 and diode D6 provide series shunt feedback whichelevates the emitter-ground voltage of transistor Q5 to approximately1.2 V, assuring that an adequate bias point is maintained for the baseof transistor Q3 through resistor R6.

Line 128' from receiver 120 supplies the 9 volt battery source 126 tothe amplifier/display circuit 140. Line 128 returns to the receivercircuit 120 to power the signal amplifier. Line 118 provides apreamplified signal from receiver 120 to amplifier/display circuit 140.Line 118' is a ground for the receiver and amplifier/display circuits.

FIG. 11B also shows the circuitry of the amplifier/display circuit 140,shown in block form in FIG. 6. The 9 volt source 126 supplies amplifierU1, filtered by capacitor C9. The signal inputted from the receiveralong line 118 is fed through capacitor C10. Diode 130, connected inseries with resistor R10, protects amplifier U1 from negative voltages.The signal is then provided to amplifier U1. Offset voltage adjustmentis provided by variable resistor R11, allowing the output of amplifierU1 as supplied to resistors R1/E and R2/E to be factory preset asdesired.

The 9 volt power source 350 (corresponding to power source 126) powersthe sensitivity switch 134 (38 in FIG. 2). Activation of thissensitivity switch 134 supplies transistor Q9 with sufficient voltage toplace the transistor in a full "on" state. Transistor Q8 is turned off.Resistor R1/C provides a shunt path for the voltage supplied to Q8 andQ9. Voltage is supplied through resistor R1/D to the positive input ofamplifier U3B, limited to approximately 0.6 V by diode D8, which isforward biased. When the switch 134 is activated, the amplifier willregulate itself such that the negative input to amplifier U3B will bedriven to a voltage equal to the positive input of amplifier U3B. Thisregulation results primarily from self-adjusting of the current throughtransistor Q10. Transistor Q10 controls the current through resistorR12, which feeds the negative input to U1. The voltage at the negativeinput to U1 is adjusted higher or lower to adjust the output of U1 toR1/E and R2/E such that the current through R1/E, R3/E, and Q9 producesa steady-state voltage input to U3B of about 0.6 V. This process resultsin a calibration of the positive input to amplifier U3A to a presetvalue. When switch 134 is deactivated, capacitor C11 is charged andtransistor Q8 is turned off such that the voltage levels at the negativeinput of U3B and the positive input of U3A are maintained at thesevalues. A 0.6 V potential is supplied to the connection between Q9 andR3/E by transistor Q8 when switch 134 is off, reducing the leakage atcapacitor C11.

Adjustment of the positive input of U3A readjusts the voltage suppliedto LCD display 34 such that the displayed output is between the minimumand maximum outputs, for example about five "bars" on a fourteen-"bar"display. Despite this readjustment, the input to the LCD display remainsproportionate to the input to amplifier U1, and thus to the strength ofthe electromagnetic signal received by the receiver.

The output of amplifier U3A is fed to an a stable multivibrator circuitincluding two parallel resistor-transistor circuits, resistors R1/A ,R1/B, R2/A, and R2/B and transistors Q6 and Q7. This circuit generatesan oscillating signal having a substantially square wave form whencapacitor C13, resistor R1/B, and resistor R2/B have valuessubstantially equal to corresponding elements C14, R1/A, and R2/A,respectively. The circuit also minimizes the effective DC voltageapplied across the inputs to LCD display 34.

With a nine-volt source supplying the circuitry, the output from themultivibrator has an effective potential difference from minimum tomaximum of approximately 18 V. This difference enhances the performanceof the LCD display, described in further detail below. The a stablemultivibrator, or square wave oscillator, also provides an accuratelow-voltage output for powering LCD 34 at voltages in the range of onevolt or less. Capacitors C13 and C14 are selected to obtain the desiredfrequency of the multivibrator square wave.

FIGS. 12A and 12B show the elements of the liquid crystal display 34including transparent conductive element 238 on a first glass element220 and transparent conductive element 240 on LCD glass backplane 230.Element 220 is comprised of resistive element 238 having a constantohms-per square throughout. The display uses standard LCD materialsincluding a low operating voltage fluid, an elastomeric connector,smooth reflective backing, and polarizers. The resistive element isconnected across pins 232 and 234, received from the display drivercircuit as indicated in FIG. 11B. Although the display indicates a rangeof values corresponding to the strength of the electromagnetic signalreceived at the receiver, only two inputs to the element are needed.

The resistive LCD element 238 winds in a series of linear segments frompin 232 to point M, as shown in FIG. 12A. In the preferred embodiment,about 440 squares (corresponding to 44 KOhms resistance at 100Ohms/square) connect pin 232 to point M. About 176 squares connect pointM to pin 234 (comprising about 17.6 KOhms at 100 ohms/square). However,the metalization process may create a resistive element having otherresistances per square which are equally appropriate for the circuit,since the resistance per square will be substantially constantthroughout the resistive element. The element 238 path from point M topin 234 comprises multiple segments connected at right angles to eachother in the embodiment shown. The path from pin 232 to point M includesabout 39 linear segments connected at right angles in the embodimentshown. The 39 segments include about 20 longer, horizontal segments,which correspond to the bars at display 34. The remainder of thesegments are short, vertical segments which bridge the horizontalsegments but are not part of the active area defined by element 240.

A varying-amplitude square wave is fed from the oscillating circuitshown in FIG. 11B and previously described to pins 232 and 234. As thevoltage across pins 232 and 234 increases, indicative of a strongerelectromagnetic signal received at the receiver, the successiveresistive squares of resistive element 238 will have higher potentialsin a direction from pin 232 to point M. For example, a voltage potentialacross pins 232 and 234 of 10 volts will have a voltage difference frompin 232 to point A of 44K*10V/(44K+17.6K)=7.14 V. Since there are 440squares from pin 232 to point M in the embodiment shown by way ofexample, each square from pin 232 to point M will have a voltagepotential which increases by 7.14 V*100/44 K , or about 0.016 V. When aparticular square has a voltage potential greater than a thresholdvoltage for the LCD element, the LCD metal traces are activated and thedisplay darkened at the location of that square. One skilled in the artwill recognize that there is a border area around the threshold voltagewhere the metal traces partially but not fully react to the potentialdifference. Increasing the potential across pins 232 and 234 will resultin a greater number of squares at or above the threshold voltage. Thus,the portion of the resistive element 238 that is at a voltage whichactivates the liquid crystal display may increase from the segmentbetween pin 232 and point N in FIG. 12A, to the segment extending frompin 232 to point P in FIG. 12A.

FIG. 12B shows display backplane 230, which is placed over displayelement 220 to present a display to the user such as the displays shownin FIG. 7 at 162, 164, 166, and 168. A relatively low voltage acrosspins 232 and 234 will activate only the first portion of the resistiveelement 238 from pin 232 to point M, corresponding to an appearance of arelatively small number of "bars" in the display screen, such as shownat display 160 or 164 in FIG. 7. As the voltage between pins 232 and 234(and thus pin 232 and point M) increases, the number of "bars" whichappear in the display increases in the upward direction, such as shownat display 166 in FIG. 7. A maximum reading will appear as a series ofseveral bars substantially filling the trapezoidal portion of cover 230,as indicated by display 162 of FIG. 7.

FIG. 13 shows the location of transmitter 10 and receiver 12 where thepoints to be located correspond to points A' and B'. A line drawn fromA' to B' is not perpendicular to surfaces 18 and 16, unlike thesituation as shown in FIG. 7. Thus, for optimum performance transmitter10 and receiver 12 are held such that transmitting surface 20 andreceiving surface 78 are normal to the linear path 200 between A' andB', rather than flush with surfaces 18 and 16, respectively, in order toachieve the best results. Otherwise, the process used is similar to theprocess described herein.

The values or product numbers of the elements described in FIGS. 11A and11B are set forth in Table A.

                  TABLE A                                                         ______________________________________                                        COMPONENT      VALUE/PRODUCT NUMBER                                           ______________________________________                                        R1, R2, R9     1.1 K Ohms                                                     R3             62 K Ohms                                                      R5, R8         20 K Ohms                                                      R6             270 K Ohms                                                     R7             150 Ohms                                                       R10            2.7 K Ohms                                                     R11            25 K Ohms (variable)                                           R12            100 Ohms                                                       R1/A, R1/B, R1/C,                                                                            10 K Ohms                                                      R1/D                                                                          R2/A, R2/B, R2/D,                                                                            220 K Ohms                                                     R2/E                                                                          L1             33 mH                                                          D1, D2, D5     1N4005                                                         D3, D6, D8     1N4148                                                         D4             1N5221B (zener)                                                D5             1N5229B (zener)                                                Diode 130      1N34A                                                          Q1, Q2, Q5, Q6,                                                                              2N4401                                                         Q7                                                                            Q3, Q4         MPSA13                                                         Q8, Q9, Q10    2N4007                                                         C1             6.8 micro F                                                    C2             .027 micro F                                                   C4             22 micro F                                                     C5             2200 pico F                                                    C6, C10, C13, C14                                                                            .01 micro F                                                    C7             .001 micro F                                                   C9             47 micro F                                                     C11, C12       .1 micro F                                                     U1             TLC271                                                         U3A, U3B       TLC272                                                         ______________________________________                                    

What is claimed is:
 1. An apparatus for locating two pointscorresponding to points located on the opposite sides of a structuralcomponent comprising:(a) a transmitter housing attachable to one side ofthe structural component for enclosing a signal transmitting means fortransmitting an electromagnetic signal; (b) a signal transmitting meansmounted in said housing for transmitting an electromagnetic signalhaving a preselected frequency up to 10 KHz and indicative of a firstpoint located on the first side of the structural component at apredetermined spacial relationship to said transmitter housing; (c) areceiver housing for enclosing a signal receiving means; (d) a signalreceiving means mounted in said receiver housing for generating anelectrical signal proportionate to the strength of the electromagneticsignal received from the transmitting means at a receiver-correspondingposition located at a predetermined spacial relationship to the receiverhousing which corresponds to a position located on the second side ofthe structural component; (e) a display housing for enclosing a displaymeans; (f) a display means for displaying a maximum-indicative readingwhen said electrical signal generated by said signal receiving meansindicates a maximum electromagnetic signal level, such that saidmaximum-indicative reading is displayed at said display means when thereceiver housing is located such that the receiver-correspondinglocation corresponds to the second point to be located; (g) electricalinterconnecting means for electrically interconnecting the electricalsignal generated by the signal receiving means to the display means; and(h) sensitivity adjusting means mounted on said display housingcomprising a push button control and electrically interconnected to thedisplay means for adjusting the readout at the display means to a valuebetween the minimum and maximum values indicated by the display meanswhen the push button control is activated.
 2. An apparatus in accordancewith claim 1 comprising location indicating means formed in theperiphery of an exterior surface of the receiver housing through whichthe receiving means receives the electromagnetic signal from thetransmitting means for indicating the location along said planar surfacewherein said electromagnetic signal is received for indicating thereceiver-corresponding position.
 3. An apparatus in accordance withclaim 2 wherein the means formed in the periphery of the exteriorsurface further comprises two pairs of intersecting point indicatingmeans formed in said exterior periphery, each pair located such that aline drawn between one pair will intersect a line drawn between theother pair at the receiver-corresponding position.
 4. An apparatus inaccordance with claim 1 wherein the electrical interconnecting meanscomprises an electrical cord connected between the receiver housing andthe display housing such that the receiver housing is capable of beinglocated in a position remote from the display housing.
 5. An apparatusin accordance with claim 4 further comprising integrating means fordetachably retaining the transmitter housing, the receiver housing, andthe display housing when the apparatus is not in use.
 6. An apparatusfor locating two points corresponding to points located on the oppositesides of a structural component comprising:(a) a transmitter housingattachable to one side of the structural component for enclosing asignal transmitting means for transmitting an electromagnetic signal andincluding an insertable portion for retainably inserting said housinginto one end of a display housing; (b) a signal transmitting meansmounted in said housing for transmitting an electromagnetic signalhaving a preselected frequency and indicative of a first point locatedon the first side of the structural component at a predetermined spacialrelationship to said transmitter housing; (c) a receiver housing forenclosing a signal receiving means; (d) a signal receiving means mountedin said receiver housing for generating an electrical signalproportionate to the strength of the electromagnetic signal receivedfrom the transmitting means at a receiver-corresponding position locatedat a predetermined spacial relationship to the receiver housing whichcorresponds to a position located on the second side of the structuralcomponent; (e) display means for displaying a maximum-indicative readingwhen said electrical signal generated by said signal receiving meansindicates a maximum electromagnetic signal level, such that saidmaximum-indicative reading is displayed at said display means when thereceiver housing is located such that the receiver-correspondinglocation corresponds to the second point to be located; and (f)electrical interconnecting means for electrically interconnecting thesignal receiving means to the display means, and including an electricalcord connected between the receiver housing and the display housing suchthat the receiver housing is capable of being located in a positionremote from the display housing; (g) a display housing for enclosing thedisplay means forming structural receiving means for receiving theinsertable portion of said transmitter housing.
 7. An apparatus inaccordance with claim 6 further comprising retaining means mounted onthe exterior of said transmitter housing, wherein the structuralreceiving means of the display housing further comprises transmitterhousing receiving means formed at one end of the display housing forreceiving said transmitter housing retaining means at said end of saiddisplay housing.
 8. An apparatus in accordance with claim 7 wherein thereceiver housing further comprises an insertable portion for retainablyinserting said housing into one end of the display housing, wherein thedisplay housing forms structural receiving means for receiving saidinsertable portion of said receiver housing at the end opposite the endforming a structural receiving means for the transmitter housing.
 9. Anapparatus in accordance with claim 8 further comprising retaining meansmounted on the exterior of said receiver housing, wherein the structuralreceiving means of the display housing further comprises means formed atthe end of the display housing opposite the transmitter housingreceiving means for receiving said receiver housing retaining means. 10.An apparatus in accordance with claim 6 further comprising batterystorage means mounted in said transmitter housing for storing a batterysuch that a battery may be inserted into said transmitter housing whensaid transmitter housing is separated into said insertable portion andsaid base portion to expose said battery storage means.
 11. An apparatusin accordance with claim 10 wherein the retaining means comprises armmembers mounted on said transmitter housing for inserting into thedisplay housing; and arm member receiving cavities formed in saiddisplay housing for receiving said arm members; wherein separation ofsaid arm members from said transmitter housing separates said insertableportion of said transmitter housing from said base portion of saidtransmitter housing.
 12. An apparatus in accordance with claim 1 furthercomprising nail receiving means formed in the transmitter housing forreceiving a nail inserted in said first side of the structural componentat said first point at a location adjacent the transmitter housingcorresponding to the area from which the electromagnetic signal isemitted from the transmitting means.
 13. An apparatus in accordance withclaim 1 further comprising transmitter strength control means forsetting the electromagnetic signal emitted by the transmitting means atone of a selected group of signal strengths.
 14. An apparatus inaccordance with claim 13 wherein the transmitter strength control meanscomprises a pair of zener diodes electrically interconnected in parallelto a switching means connected to a power source and having a high stateand a low state such that the switching means provides a high stateoutput at a voltage substantially equal to the sum of the reverse-biasvoltages of the pair of zener diodes, and a low state output at avoltage substantially equal to the sum of the forward-bias voltage ofone zener diode and the reverse-bias voltage of the other zener diode.15. An apparatus in accordance with claim 1 wherein the transmittingmeans comprises a power source remote from the display housing andreceiver housing; an oscillator powered by said power source forsupplying an electrical signal to a transmit coil for generating anelectromagnetic signal, and a transmit coil electrically connected tosaid oscillator for producing an electromagnetic signal at apredetermined frequency.
 16. An apparatus in accordance with claim 1wherein the receiver means further comprises a pick-up coil forreceiving an electromagnetic signal and converting the signal into anelectrical signal; and amplifying means electrically connected to saidpick-up coil for amplifying the electrical signal generated at thepick-up coil.
 17. An apparatus in accordance with claim 16 wherein thesensitivity adjusting means further comprises gain setting meanselectrically connected to said amplifying means for setting theelectrical signal amplification at said amplifying means.
 18. Anapparatus in accordance with claim 1 wherein the display means comprisesa liquid crystal display.
 19. An apparatus for locating two pointscorresponding to points located on the opposite sides of a structuralcomponent comprising:(a) a transmitter housing attachable to one side ofthe structural component for enclosing a signal transmitting means fortransmitting an electromagnetic signal; (b) a signal transmitting meansmounted in said housing for transmitting an electromagnetic signalhaving a preselected frequency and indicative of a first point locatedon the first side of the structural component at a predetermined spacialrelationship to said transmitter housing; (c) a receiver housing forenclosing a signal receiving means; (d) a signal receiving means mountedin said receiver housing for generating an electrical signalproportionate to the strength of the electromagnetic signal receivedfrom the transmitting means at a receiver-corresponding position locatedat a predetermined spacial relationship to the receiver housing whichcorresponds to a position located on the second side of the structuralcomponent; (e) display means for displaying a maximum-indicative readingwhen said electrical signal generated by said signal receiving meansindicates a maximum electromagnetic signal level, such that saidmaximum-indicative reading is displayed at said display means when thereceiver housing is located such that the receiver-correspondinglocation corresponds to the second point to be located, comprising(i) apair of display inputs having a voltage potential proportionate to thestrength of the electromagnetic signal; and (ii) a resistive elementconnected across the pair of display inputs, the resistive elementforming a first set of element segments substantially parallel to eachother, each element segment connected at one end to one adjacent elementsegment and at the other end to a second adjacent element segment by asecond set of element segments positioned substantially perpendicular tosaid first set of element segments; and (f) electrical interconnectingmeans for electrically interconnecting the signal receiving means to thedisplay means.
 20. An apparatus in accordance with claim 19 wherein thesignal receiving means further comprises oscillating means for providingsaid pair of display inputs with a substantially square oscillatingsignal having an amplitude proportionate to said electrical signal. 21.An apparatus in accordance with claim 20 wherein the oscillating meanscomprises an astable multivibrator.
 22. An apparatus in accordance withclaim 19 wherein said first set of element segments comprises relativelylong, linear elements and said second pair of element segments comprisesrelatively short, linear segments.
 23. An apparatus in accordance withclaim 22 wherein the display means further comprises a display coverforming a trapezoidal window and substantially covering said second setof element segments such that said first set of element segments appearsthrough said window in the form of a series of substantially parallel,unconnected segments.
 24. An apparatus for locating two pointscorresponding to points located on the opposite sides of a structuralcomponent comprising:(a) a transmitter housing attachable to one side ofthe structural component for enclosing a signal transmitting means fortransmitting an electromagnetic signal; (b) a signal transmitting meansmounted in said housing for transmitting an electromagnetic signalhaving a preselected frequency up to 10 KHz and indicative of a firstpoint located on the first side of the structural component at apredetermined spacial relationship to said transmitter housing; (c) areceiver housing for enclosing a signal receiving means; (d) a signalreceiving means mounted in said receiver housing for generating anelectrical signal proportionate to the strength of the electromagneticsignal received from the transmitting means at a receiver-correspondingposition located at a predetermined spacial relationship to the receiverhousing which corresponds to a position located on the second side ofthe structural component; (e) display means for displaying amaximum-indicative reading when said electrical signal generated by saidsignal receiving means indicates a maximum electromagnetic signal level,such that said maximum-indicative reading is displayed at said displaymeans when the receiver housing is located such that thereceiver-corresponding location corresponds to the second point to belocated; and (f) electrical interconnecting means for electricallyinterconnecting the electrical signal generated by the signal receivingmeans to the display means comprising a cord insertable into thereceiver housing and electrically connectable to the display means andsignal receiving means, said cord having a first interconnection meansfor supplying power to the display means from a power source located inthe receiver housing, and a second interconnection means for supplyingpower received at a display means from the first interconnection meansto the signal receiving means, such that power is supplied to the signalreceiving means and the display means when the cord is inserted into thereceiver housing and electrically connected to the receiving means anddisplay means.